Oxygen generation within apparatus by way of chemical reaction is known. For example, chemical oxygen generators employing alkali metal chlorates are described in U.S. Pat. Nos. 3,702,305; 2,469,414; 2,558,756; 2,775,511; 3,207,695; 3,276,846 and 3,233,187; oxygen generation occurs in these generators at elevated temperature in excess of 200° C. as metal chlorate therein is reduced to its corresponding metal chloride.
In U.S. Pat. No. 5,750,077, there is described a device for delivering breathable oxygen, the device utilising an endothermic reaction wherein potassium chlorate (KClO3) is catalyzed in the presence of manganese dioxide (MnO2) to yield potassium chloride (KCl) and oxygen gas. In the device, the endothermic reaction is initiated by using battery-powered resistive heating fingers which, in operation, heat the KClO3 and the MnO2 to at least 200° C. above which the reaction is exothermic and thus self-sustaining. The device comprises a battery for initiating the reaction, a replaceable oxygen generating canister including the KClO3 and MnO2 materials, and a filter canister. The battery is designed to connect onto a first end of the oxygen generating canister. The filter canister is designed to couple onto a second end of the oxygen canister remote from the first end. The filter canister is in gaseous communication with the oxygen generating canister and is connected via an oxygen flow tube to a face mask of the device for interfacing to a user's face whereat the oxygen is dispensed. The filter canister includes a carbon filter for removing impurities and for inhibiting reactant transmission from the oxygen generating canister to the face mask and hence to the user. Moreover, the oxygen generating canister includes a composite thermal insulator comprising metallized thin films interspersed with low thermal-conductivity foams for insulating the potassium chlorate and manganese dioxide materials from ambient environment.
In U.S. Pat. No. 3,736,104, electrically and chemically initiated thermal oxygen generators are described, the generators operable to deliver oxygen at their associated outlet tubes at a relatively high temperature oxygen in a range of 210° C. to 238° C. rendering the oxygen unsuitable for direct human inhalation.
Thermal management in the aforementioned oxygen generators represents a problem which is considered in U.S. Pat. No. 5,620,664. In this patent, a portable dispenser of medically pure oxygen is described. The dispenser includes a disposable oxygen generator comprising a compressed metal chlorate or oxide briquette of hexagonal cross-section having first and second tapered ends, the first end including a recess therein for receiving a water-activatable ignition material in the form of an ignition cone. Water for activating the ignition material is provided from a sealed water-filled chamber. In order to bring the briquette into operation, a user depresses a user-actuated ignition pin which punctures the chamber for releasing the water therein onto the ignition material which subsequently ignites and, in turn, ignites the briquette. The dispenser also includes a helical tubular coil through which oxygen generated by the briquette is passed for providing corresponding cooled oxygen which is delivered to the user.
In the portable dispenser, a region surrounding the briquette is devoid of insulation allowing uninhibited heat radiation from the briquette. However, the briquette is provided with supporting mats at the first and second ends thereof for mechanically clamping the briquette within the dispenser. The briquette is tapered at its first end in the vicinity of the ignition material to prevent sudden oxygen outpouring when the reaction within the briquette is initiated. As the reaction within the briquette proceeds, the temperature of the briquette tends to increase which accelerates the reaction, the tapered second end providing a reducing reaction cross-sectional area which assists to reduce the rate of reaction and thereby maintain a more constant oxygen delivery rate from the dispenser as the briquette is consumed.
Thus, there arises a first problem that thermal insulation included around the briquette increases briquette temperature on account of thermal energy being retained within the briquette. Such retention causes an increased rate of reaction within the briquette with an associated increased rate of oxygen generation. Conversely, an absence of thermal insulation results in the dispenser becoming relatively hot at its peripheral surface in use. Moreover, uniform oxygen generation rate is a second problem which arises in known oxygen generators. The present invention has been devised to address at least one of the first and second problems.